Prentice.Hall.Introduction.to.Java.Programming,.Brief.Version.9th.(2014).[sharethefiles.com]

586 Chapter 15 Abstract Classes and Interfaces
create a Rational
create a Rational
add
5 Rational r1 = new Rational(4, 2);
6 Rational r2 = new Rational(2, 3);
7
8 // Display results
9 System.out.println(r1 + " + " + r2 + " = " + r1.add(r2) );
10 System.out.println(r1 + " - " + r2 + " = " + r1.subtract(r2) );
11 System.out.println(r1 + " * " + r2 + " = " + r1.multiply(r2) );
12 System.out.println(r1 + " / " + r2 + " = " + r1.divide(r2) );
13 System.out.println(r2 + " is " + r2.doubleValue() );
14 }
15 }
2 + 2/3 = 8/3
2 - 2/3 = 4/3
2 * 2/3 = 4/3
2 / 2/3 = 3
2/3 is 0.6666666666666666
The main method creates two rational numbers, r1 and r2 (lines 5–6), and displays the
results of r1 + r2, r1 - r2, r1 x r2, and r1 / r2 (lines 9–12). To perform r1 + r2,
invoke r1.add(r2) to return a new Rational object. Similarly, invoke r1.subtract(r2)
for r1 - r2, r1.multiply(r2) for r1 x r2 , and r1.divide(r2) for r1 / r2.
The doubleValue() method displays the double value of r2 (line 13). The double-
Value() method is defined in java.lang.Number and overridden in Rational.
Note that when a string is concatenated with an object using the plus sign (+), the object’s
string representation from the toString() method is used to concatenate with the string. So
r1 + " + " + r2 + " = " + r1.add(r2) is equivalent to r1.toString() + " + "
+ r2.toString() + " = " + r1.add(r2).toString().
The Rational class is implemented in Listing 15.13.
LISTING 15.13
Rational.java
1 public class Rational extends Number implements Comparable {
2 // Data fields for numerator and denominator
3 private long numerator = 0;
4 private long denominator = 1;
5
6 /** Construct a rational with default properties */
7 public Rational() {
8 this(0, 1);
9 }
10
11 /** Construct a rational with specified numerator and denominator */
12 public Rational(long numerator, long denominator) {
13 long gcd = gcd(numerator, denominator);
14 this.numerator = ((denominator > 0) ? 1 : -1) * numerator / gcd;
15 this.denominator = Math.abs(denominator) / gcd;
16 }
17
18 /** Find GCD of two numbers */
19 private static long gcd(long n, long d) {
20 long n1 = Math.abs(n);
21 long n2 = Math.abs(d);
22 int gcd = 1;